Wildlife and global warming
Navigating the
Arctic Meltdown
© KEN CURTIS
wo lve r i n e s
S
ympathy for the tough, tenacious “devil bear,” as the wolverine is also known, has never been
widespread. That could change soon, as rising temperatures prematurely melt the deep, high-alti-
tude, snow-pack dens where these misunderstood and already rare mammals nurture their young.
With fewer than 1,000 left in the contiguous 48 states, wolverines may be one of the rarest
carnivores in North America. Low population densities and large home ranges make them sensitive
to habitat disturbance and fragmentation—and difficult to study.
The names given to this creature of mountain forest
and tundra indicate how poorly understood it is and
why it was once persecuted by hunters. “Wolverine”
and “devil-bear” are the ones most commonly used. It
is not closely related to the wolf—or to Satan—but it
does have a reputation for thievery and ferocity. The
French call it carcajou, Inuit for “evil spirit.” To the
Cree, it is ommeethatsees or “one that likes to steal”; to
scientists, it is Gulo gulo, Latin for “the glutton.” Their
fierce reputation does have some basis in fact: Researchers in one study found two radio-collared wolverines
that died in fights with black bears 10 times their size.
Most evidence indicates, however, that wolverines
avoid confrontations with larger mammals—including
humans. In fact, the mere presence of people in their
habitat easily disturbs them.
Yet another moniker, “skunk bear,” somewhat better
describes the wolverine’s appearance and behavior. The
wolverine is a medium-sized carnivore with a stocky build
like a bear’s, and, like the skunk, has dark, shaggy fur with
wide, lighter colored stripes running down its back. Like
skunks, they mark their food and territory with strongsmelling secretions. Their closest relatives are actually
weasels, badgers, ferrets, martens, fishers and otters, fellow
members of the Mustelid family. Wolverines are the largest
and rarest terrestrial members of this family.
© norbert rosing/animals animals
With its shaggy, coarse, striped fur, the wolverine resembles a cross
between a skunk and a small bear, hence the nickname, “skunk bear.”
The home ranges for these typically solitary wanderers
are the largest reported for a carnivore of their size, rivaling
those of bears, wolves and cougars in many areas. Given
their need for huge tracts of habitat, wolverines probably
always existed in low numbers and at very low densities. In
the contiguous United States, they live exclusively in the
Rocky Mountains and the Pacific coast range. Even there
their hold is tenuous: perhaps 600 to 700 in Montana,
Idaho and Wyoming, another 100 or so in the North
Cascades of Washington.
In winter, wolverines spend much of their time in the
coniferous forests of the mountains. In summer, they move
up to the rock- and talus-covered slopes above the tree
line—probably to avoid summer heat.
Wolverines prey on a large variety of small mammals,
including squirrels, marmots, pikas, hares and even porcupines. They are less effective predators of larger mammals
such as deer, elk and caribou, however, and rely on the
hunting advantages deep snow offers. They also depend
heavily on animals killed by harsh winter conditions or
wounded by hunters. They often bury any excess or stash it
in rocky crevices or trees.
Low prey densities and inhospitable conditions limit
wolverine populations, which probably explains the unusually large home ranges of these carnivores. One study in
Arctic Canada found that average home-range size was about
50 square miles for females, 150 square miles for males. In
the rugged mountains of the greater Yellowstone area, each
animal requires even more territory: females nearly 300
square miles and males 350 square miles. Reported ranges
in Idaho are 175 square miles for females and 719 square
miles for males. These ranges do overlap—a single male’s
territory, for example, often includes parts of the ranges of
several different females—but overall they exist at very low
densities. It is not unusual for wolverines to travel 20 miles
per day in search of food.
The availability of food also governs wolverine reproduction. Wolverines reproduce through “delayed implantation.”
The egg is fertilized, but its development temporarily stops.
It then floats in the uterus, implanting only when food
supply, human disturbance level and other environmental
conditions are acceptable. This reproductive mechanism
allows wolverines to have their young when food is most
abundant and to adjust the size of the litter, an effective way
of reproducing without sacrificing precious energy.
Females den in high mountain cirque basins, digging
deep into the snow in areas protected by logs and boulders.
Substantial snow pack is essential to insulate and protect
these dens where the young are born. In interior and
northern Alaska, wolverine-excavated snow caves include
one or two tunnels up to 60 yards long. Kits are usually
born in January or February and remain in the den for 12 to
14 weeks. Wolverines reach adult size when they are seven
months old, but they do not breed until they are two or
three years old.
Fragmentation of habitat is one of the threats to the
wolverine. In the contiguous United States, wolverines
prefer high-elevation, subalpine communities, which means
their habitat is naturally limited by geography. Roads and
human developments introduce vehicle strikes as a source
of wolverine mortality and carve up this already fragmented
habitat, hindering wolverine movements, severing the rather
tenuous connections between habitats and further isolating
small groups of wolverines. In the Rocky Mountains, the
wolverine population is now splintered into a half-dozen or
so subpopulations of 50 to 200 animals, which may be too
small to persist for long.
Wolverine fur is frost resistant, making it a popular
trim for parka hoods, thus trapping is another source of
mortality for the species. Wolverine trapping is still legal in
Montana, one of the animal’s last strongholds in the lower
48 states. In Montana’s Pioneer Range, trapper harvest
U.S.D.A. FOREST SERVICE
Glacier National Park has the winterlong snow cover wolverines prefer.
North American Distribution of the Wolverine
Source: the wolverine foundation, Inc.
60N
60W
90W
120W
150W
30N
Wolverine range (purple areas on map) includes the mountainous regions of Idaho, Montana, Wyoming, Washington and British Columbia, and all of
Alaska and northern Canada. A separate wolverine subspecies occurs in northern Europe and Asia.
accounted for six of the 12 wolverines that died during
the course of a research study. Wolverine trapping is also
allowed in Alaska.
Recreation, especially during the denning season, is
re reviewed and refined by participants at the Defenders 2002 Wolverine Workshop,
Wolverine Foundation, Inc. offers
this
map as a representation
also
detrimental
to wolverines. The species is so sensimakes no claims as to its accuracy.
tive to human disturbance that cross-country skiing and
snowshoeing, let alone snowmobiling, can drive a mother
to move her kits to another location. The tremendous
increase of snowmobiling in wolverine habitat in recent
years is of particular concern. “Female wolverines appear
to be most sensitive to human presence during the denning
period,” U.S. Forest Service wolverine biologist Jeff
Copeland told attendees at Carnivores 2006, the biannual
predator conservation conference sponsored by Defenders of Wildlife. Bob Inman, studying wolverines in the
Yellowstone area, agrees: “If females are expending energy
to avoid humans in the winter, that would definitely affect
their reproductive success.”
Warming Trends
Global warming threatens to eliminate mountaintop habitat
at the southern edges of wolverine range, a serious loss for a
species already holding on tenuously. Seasonal movements of
wolverines farther up mountain slopes appear to be linked to
intolerance of high temperatures. Global warming is likely
to increase summer temperatures, effectively shrinking the
wolverine’s range and possibly hindering travel to find mates.
In winter, the snow pack is likely to move 300 feet upslope
for every degree of warming. In parts of the American West,
snow seasons that now average four months long now would
shrink to less than three months in 20 years, and down to two
months in 40 years.
All Rights Reserved, The Wolverine Foundation, Inc., 2004
Deep snow pack lasting long into early spring seems
to be important for wolverines, because it provides secure,
well-insulated dens in which to raise their kits. At the
Carnivores 2006 conference, wolverine researchers warned
that receding snowlines could significantly reduce quality
denning habitat. Mild winters also potentially affect food
availability for wolverines. The species depends extensively
on winter-killed carrion and the advantages that deep snow
offers for hunting ungulates.
Preparing for the meltdown
To ensure that wolverines continue to roam the remote
wild lands of North America, we must act now to reduce
the emission of greenhouse gases. We also must take
other important steps now to help the wolverine navigate a looming bottleneck of complex threats posed by
climate change.
•P
rotect the wolverine under the Endangered Species
Act. We must continue to press for strict federal protection of wolverines. Such protection is crucial because
wolverine populations have low resiliency due to their
rarity and low reproductive rates, making it difficult
for them to rebound from numbers lowered by natural
or human-influenced factors. In 2000, Defenders of
Wildlife and other groups petitioned the U.S. Fish and
Wildlife Service to protect wolverines in the lower 48
states under the Endangered Species Act. In 2003, the
Bush administration denied the petition, citing insufficient evidence of declines. Defenders successfully
challenged that decision in court, and the government is
now reconsidering listing the wolverine.
• Protect wolves throughout wolverine range. During
mild winters, fewer deer, elk and moose die from starvation and cold-related stress—good news for the ungulates,
bad news for scavengers that rely on carrion. Researchers
in Yellowstone National Park found that wolves aid several
species of scavengers—from magpies to grizzlies—during
mild winters, because they are active and effective predators year-round, which means a reliable supply of carrion.
Wolves thus “extend the timescale over which scavenger
species can adapt to the changing environment.” To date,
wolverines in Yellowstone have not been observed feeding
on wolf kills, but as global warming lessens the intensity
of winters, wolf kills may become an important source of
food for wolverines.
• Control trapping. Montana and Alaska allow wolverine trapping, although it provides little economic
benefit and is a worrisome source of wolverine mortality. The wildlife agencies in these states must monitor
not only harvest numbers, but also sex and age ratios
and the impact of trapping on the total wolverine
population, and adjust seasons, bag limits and other
regulations accordingly.
•R
estrict snowmobile use in wolverine habitat in national
parks and roadless areas. Areas where wolverines are likely
to be denning should be off limits to motorized recreation,
such as snowmobiling and helicopter skiing. Other precautions may be necessary as the mountain snow pack shrinks
and wolverines and people come into closer contact,
causing additional disturbance that can negatively affect
breeding success.
•P
rotect existing large areas of habitat from logging and
development. We must safeguard the forested corridors
adjacent to logging roads that wolverines may use to get to
other parts of their home ranges. Large protected tracts, such as
national forest roadless areas, are critical as sources for wolverine dispersal to other regions. We must also address the threat
posed by trappers who use these roads to set their traps.
• Restore linkages where roads cross valleys between mountainous areas. Roads that permit human access to wolverine
habitat can be detrimental to wolverine populations, especially in areas where trapping or hunting is allowed. Major
roads, such as the Trans-Canada Highway, can also block
wolverines from reaching important parts of their habitat.
• Conduct research. The wolverine, still one of the country’s
least understood carnivores, was precluded from listing
under the Endangered Species Act twice within the past 10
years for lack of adequate information. We need more data
on population size, ecology and optimal denning habitat.
We also need a better understanding of wolverine range and
movements to inform the design and placement of road
crossings and corridors between key habitats. All research
must be done with care as even the presence of researchers
can cause wolverines to abandon their dens.
Re fe re nces
Alaska Department of Fish and Game,
“Wolverine”; available from http://www.adfg.
state.ak.us/pubs/notebook/furbear/wolverin.
php; Internet; accessed 7 February 2007.
Snow Dependent Species—A Case for the
Wolverine.” Paper presented at Carnivores
2006, St Petersburg, Florida, 12-15 November
2006.
Copeland, Jeffrey P. “Biology of the Wolverine
in Central Idaho.” M.S. thesis, University of
Idaho, Moscow. 1996. 138 pp.
Hinterland’s Who’s Who. Available from http://
www.hww.ca/hww2.asp?id=108; Internet;
accessed 7 February 2007.
Copeland, Jeffrey P., Keith Aubry, Kevin
McKelvey, and Steven W. Running. “The
Implications of Global Warming on a
Tolme, Paul. “Sympathy for the Devil Bear.”
Defenders, Winter 2006, pp 8-13.
Wilmers, Christopher C. and Wayne M. Getz.
“Gray Wolves as Climate Change Buffers in
Yellowstone.” PLoS Biology 3 no. 4 (2005).
Wilson, Don E. 1982. “Wolverine.” In Joseph
A. Chapman and George A. Feldhamer, eds.
Wild Mammals of North America: Biology,
Management, and Economics. Baltimore: Johns
Hopkins University Press, 1982.
Defenders of Wildlife
1130 17th Street, N.W. | Washington, D.C. 20036 | 202-682-9400
www.defenders.org